The present application claims priority to Japanese Patent Application No. P2001-067238 filed on Mar. 9, 2001, herein incorporated by reference.
The present invention relates to a display unit and a method of fabricating the display unit. More specifically, the present invention relates to a display unit including a plurality of micro-sized semiconductor light emitting devices arrayed on a plane of a base body at intervals and a method of fabricating the display unit.
Display units of a type using light emitting diodes (LEDs) as a light emitting source, as shown in FIG. 10, are known. FIG. 10 is a perspective view showing a rear side of an essential portion of one example of such related art display units. Referring to this figure, a display unit 100 is fabricated by two-dimensionally, densely arraying expensive LED modules 102, the size of each of which is standardized into a relatively large value (for example, 5 mm square), on a plane 101 of a base body and fixing them thereon, and connecting an anode electrode 103 and a cathode electrode 104 of each of the LED modules 102 to wiring provided on the base body by wire bonding or soldering. This related art display unit 100 has the following problem. An LED chip having a size being usually about 0.3 mm square cut out of a compound semiconductor wafer is used for the LED module 102 per one pixel, and therefore, a large number of the compound semiconductor wafers are required to provide the LED chips used for several hundreds of thousands of pixels constituting the full-screen of the display unit 100, with a result that the material cost is raised. Another problem of the related art display unit 100 is that since additional equipment and working steps are required for arraying and fixture of the LED modules and connection of the electrodes to wiring by wire bonding or soldering, the fabrication cost is essentially raised.
Each of the LED chips used for the related art display unit 100 has been usually of a planar type typically shown in FIG. 11, wherein a p-type semiconductor 106 having a p-electrode 107 and an n-type semiconductor 108 having an n-electrode 109 are stacked in a plane structure with an active layer 105 sandwiched therebetween. Light emitted from the active layer 105 is basically directed in omni-directions; however, due to a relationship between a relatively large refractive index of the semiconductor and an incident angle from the interior of the semiconductor to the interface (surface), light directed in the vertical direction is mainly emerged to the outside through the interface. As a result, there occur problems that the light emission efficiency in the downward direction is low even in consideration of the fact that the light directed upwardly (rear surface side) is reflected from an electrode plane or the like to the lower side (front surface side), and that the light emitted to the rear surface side is made incident on the adjacent LED module to cause bleeding in an image displayed on the display unit.
As one specific related art example, a display unit capable of reducing the cost and improving the reliability by using light emitting diodes buried in an insulating material has been disclosed in Japanese Patent Laid-open No. Sho 57-45583. The light emitting diode used in this display unit, however, is a light emitting diode chip having a planar structure cut out of a wafer, and an anode electrode and a cathode electrode have been mounted on each of the chips in the wafer state. Also, an epoxy resin used as an insulating layer to bury spaces among the light emitting diodes fixedly arrayed on a substrate is poured and cured such that the upper surface of the insulating layer is substantially at the same level as the upper end surfaces of the light emitting devices, and the upper surface of the insulating layer is smoothened by lapping or the like.
Japanese Patent Laid-open No. Hei 3-35568 has disclosed a light emitting diode having a small pn-junction region, wherein an upper end side of a semiconductor portion taken as an optical path over the pn-junction is cut into a truncated pyramid shape in order to significantly improve the rate of light emerged outwardly from the inside of the light emitting diode through the interface between the light emitting diode and an outer transparent plastic. The refractive index of the light emitting diode is greatly different from that of the transparent plastic around the light emitting diode. Accordingly, of light directed from a point light source to the interface, a light component entering the interface in the direction perpendicular to the interface, that is, at an incident angle of 0xc2x0 and a light component having an incident angle smaller than a conical angle (for example, 27xc2x0) centered at the point light source pass through the interface; however, other light components each having a large incident angle are reflected from the interface and thereby impossible to be emerged outwardly from the inside of the light emitting diode, and are repeatedly reflected from the interface to be decayed. The cutting the upper end side of the semiconductor portion into the truncated pyramid shape is made to avoid such a phenomenon as much as possible.
Japanese Patent Laid-open No. Hei 11-75019 has disclosed a light source unit using light emitting diodes, wherein a tilt mirror tilted at 45xc2x0 is provided at a position over a semiconductor chip as the light emitting diode. The mirror is provided for allowing light emitted upwardly from the light emitting diode to be reflected from the mirror at right angles, that is, toward the horizontal direction, and as such a mirror, there is used a dichroic mirror for reflecting light emitted from the light emitting diodes for emission of light of blue, green, and red onto the same optical axis.
The present invention provides a display unit fabricated at a low cost by arraying micro-sized semiconductor light emitting devices at intervals and simply fixing them thereon, and a method of fabricating the display unit. The present invention provides a display unit that includes semiconductor light emitting devices each of which is of a micro-size and has a sufficient luminance, and a method of fabricating the display unit.
According to an embodiment of the invention, there is provided a display unit including a plurality of semiconductor light emitting devices mounted in array on a plane of a base body. The semiconductor light emitting devices are fixedly arrayed on the plane of the base body at intervals in a state being buried in a first insulating layer or in a bare state being not buried in the first insulating layer; a second insulating layer is formed on the plane of the base body so as to cover the semiconductor light emitting devices; and an upper end side electrode and a lower end side of each of the semiconductor light emitting devices are extracted via connection holes formed in specific positions of the first insulating layer and the second insulating layer.
With this display unit, since the semiconductor light emitting devices are fixedly arrayed on the plane of the base body at intervals in a state being buried in the first insulating layer or in a bare state being not buried in the first insulating layer, and the electrodes of each of the semiconductor light emitting devices are extracted via the connection holes formed in the second insulating layer covering the semiconductor light emitting devices, it is possible to significantly reduce the cost per unit area of the display unit.
According to an embodiment of the invention, there is provided a display unit, wherein the semiconductor light emitting devices are fixedly arrayed on the plane of the base body in a state being buried in the first insulating layer except the upper end portions and the lower end portions of the semiconductor light emitting devices; the upper end side electrode and the lower end side electrode of each of the semiconductor light emitting devices are extracted to the upper surface of the first insulating layer and then extracted to the upper surface of the second insulating layer; and either of the electrodes is led to a connection electrode provided on the plane of the base body. With this display unit, since each of the semiconductor light emitting devices is buried in the first insulating layer to form a resin-covered chip having a large size, it is possible to facilitate the handling of the semiconductor light emitting device, and since one electrode is connected to a drive circuit on the upper surface of the second insulating layer and the other electrode is connected to a drive circuit on the plane of the base body, the drive circuits for the electrodes located in the directions perpendicular to each other do not cross each other, so that it is possible to simplify the wiring.
According to an embodiment of the invention, there is provided a display unit, wherein the semiconductor light emitting devices are fixedly arrayed on the plane of the base body in the state being bared; the second insulating layer is formed on the plane of the base body so as to cover the semiconductor light emitting devices; the upper end side electrode and the lower end side electrode of each of the semiconductor light emitting devices are extracted to the upper surface of the second insulating layer; and either of the electrodes is led to a connection electrode provided on the plane of the base body. With this display unit, since the first insulating layer in which the semiconductor light emitting devices are to be buried is not provided, some ingenuity is required in handling the semiconductor light emitting devices; however, it is possible to omit the device burying step, and since one electrode is connected to a drive circuit on the upper surface of the second insulating layer and the other electrode is connected to a drive circuit on the plane of the base body, the drive circuits for the electrodes located in the directions perpendicular to each other do not cross each other, thereby simplifying the wiring.
According to an embodiment of the invention, there is provided a display unit, wherein each of the first insulating layer and the second insulating layer is made from a polymer compound formable into a coating film, the polymer compound includes a polyimide resin, an ultraviolet curing resin, an epoxy resin, a synthetic rubber and/or the like. With this display unit, it is possible to easily form the insulating layer even on the plane, having a large area, of the base body by coating, and hence to simplify the mounting of the semiconductor light emitting devices on the plane of the base body.
According to an embodiment of the invention, there is provided a display unit, wherein each of the semiconductor light emitting devices mainly emits light in a direction from a light emission region to the lower end plane, mounted on the plane of the base body, of the semiconductor light emitting device; and the semiconductor light emitting device has, at a position over the light emission region, a reflection mirror from which the light is reflected downwardly. With this display unit, it is possible to effectively direct light from the light emission region to the lower end plane of the semiconductor light emitting device by means of the reflection mirror.
According to an embodiment of the invention, there is provided a display unit, wherein the semiconductor light emitting device is formed into a pyramid shape or a truncated pyramid shape; and any one of at least tilt planes among planes of the pyramid or truncated pyramid shaped semiconductor light emitting device is taken as the reflection mirror. With this display unit, since the tilt planes of the polygonal pyramid or the truncated polygonal pyramid can be taken as reflecting planes, or the upper plane of the truncated polygonal pyramid can be taken as a reflection mirror, it is possible to concentrate light emitted from the light emission region to the lower end plane of the semiconductor light emitting device.
According to an embodiment of the invention, there is provided a display unit, wherein the semiconductor light emitting device is made from a gallium nitride based semiconductor having a hexagonal system; and the semiconductor light emitting device includes an active layer formed in parallel to a (1-101) plane. With this display unit, since a light emission efficiency of the active layer formed in parallel to the (1-101) plane of the gallium nitride based semiconductor is high and an electrode plane provided on the (1-101) plane can be taken as a reflection mirror, it is possible to enhance the light emission characteristic.
According to an embodiment of the invention, there is provided a display unit, wherein the semiconductor light emitting device is made from a gallium nitride based semiconductor formed by crystal growth on a growth substrate into a hexagonal pyramid shape or a truncated hexagonal pyramid shape with a (0001) plane taken as the lower end plane and (1-101) planes and planes equivalent thereto taken as the tilt planes; and the semiconductor light emitting device includes an active layer formed in parallel to the (1-101) planes and planes equivalent thereto. With this display unit, since the light emission efficiency of the active layer formed in parallel to the (1-101) plane of the gallium nitride based semiconductor is high and an electrode plane provided on the (1-101) plane can be taken as a reflection mirror, it is possible to concentrate light emitted from the light emission region to the lower end plane of the semiconductor light emitting device and particularly enhance the light emission characteristic.
According to an embodiment of the invention, there is provided a display unit, wherein the display is an image display unit or a lighting unit including an array of only one kind of the semiconductor light emitting devices allowing emission of light of a single color, or an array of a combination of a plurality of kinds of the semiconductor light emitting devices allowing emission of light of different colors. Such a display unit can usable as an image display unit or a lighting unit having a high luminance, which includes light emitting diodes or semiconductor lasers.
According to an embodiment of the invention, there is provided a method of fabricating a display unit including a plurality of semiconductor light emitting devices on a plane of a base body. The method includes the steps of burying the semiconductor light emitting devices in a first insulating layer, forming specific connection holes in the first insulating layer, and extracting an upper end side electrode and a lower end side electrode of each of the semiconductor light emitting devices via the connection holes formed in the first insulating layer; fixedly arraying semiconductor light emitting devices, from each of which the electrodes have been extracted, on the plane of the base body at intervals; forming a second insulating layer so as to cover the semiconductor light emitting devices each of which has been buried in the first insulating layer; and forming specific connection holes in the second insulating layer, and extracting the upper end side electrode and the lower end side electrode of each of the semiconductor light emitting devices having been extracted to the upper surface of the first insulating layer via the connection holes. With this method of fabricating a display unit, since each of the semiconductor light emitting devices is buried in the first insulating layer to form a resin-covered chip having a large size, it is possible to facilitate the handling of the light emitting devices and hence to easily array the light emitting devices on the plane of the base body at intervals, and since the second insulating layer is formed so as to cover the light emitting devices and then the electrodes of each of the light emitting devices are extracted via the connection holes formed in the second insulating layer and connected to drive circuits, it is possible to provide the display unit capable of significantly reducing the cost per unit area of the display unit.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein each of the semiconductor light emitting devices is buried in the first insulating layer except an upper end portion and a lower end plane thereof, and the upper end side electrode and the lower end side electrode are extracted to the upper surface of the first insulating layer. With this method of fabricating a display unit, it is possible to provide the display unit capable of facilitating the extraction of the upper end side electrode, and preventing a reduction in light emission area due to extraction of the lower end side electrode to the lower end plane.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein the upper end side electrode and the lower end side electrode of each of the semiconductor light emitting devices having been extracted to the upper surface of the first insulating layer are both extracted to the upper surface of the second insulating layer; and either of the electrodes is led to a connection electrode provided on the plane of the base body. With this method of fabricating a display unit, since one electrode is connected to a drive circuit on the upper surface of the second insulating layer and the other electrode is connected to a drive circuit on the plane of the base body, the drive circuits for the electrodes located in the directions perpendicular to each other do not cross each other, so that it is possible to provide the display unit capable of simplifying the wiring.
According to an embodiment of the invention, there is provided a method of fabricating a display including a plurality of semiconductor light emitting devices mounted in array on a plane of a base body The method includes the steps of fixedly arraying the semiconductor light emitting devices on the plane of the base body at intervals in a state being bared; forming a second insulating layer on the plane of the base body so as to cover the semiconductor light emitting devices; and forming specific connection holes in the second insulating layer, and extracting an upper end side electrode and a lower end side electrode of each of the semiconductor light emitting devices via the connection holes. With this method of fabricating a display unit, since the semiconductor light emitting devices, each of which is in the state being bared, that is, with its size not enlarged, are arrayed on the plane of the base body at intervals, some ingenuity is required in handling the semiconductor light emitting devices; however, it is possible to omit the device burying step, and to significantly reduce the cost per unit area of the display unit.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein the upper end side electrode and the lower end side electrode of each of the semiconductor light emitting devices in the state being bared are extracted to the upper surface of the second insulating layer; and either of the electrodes is led to a connection electrode provided on the plane of the base body. With this method of fabricating a display unit, it is possible to prevent a reduction in light emission area due to extraction of the lower end side electrode to the lower end plane of the semiconductor light emitting device. Also, since one electrode is connected to a drive circuit on the upper surface of the second insulating layer and the other electrode is connected to a drive circuit on the plane of the base body, the drive circuits for the electrodes located in the directions perpendicular to each other do not cross each other. As a result, it is possible to simplify the wiring.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein each of the first insulating layer and the second insulating layer is made from a polymer compound formable into a coating film, the polymer compound includes a polyimide resin, an ultraviolet curing resin, an epoxy resin, a synthetic rubber and/or the like. With this method of fabricating a display unit, it is possible to easily form the insulating layer even on the plane, having a large area, of the base body by coating, and hence to simplify the mounting of the semiconductor light emitting devices on the plane of the base body.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein each of the semiconductor light emitting devices mainly emits light in a direction from a light emission region to the lower end plane, mounted on the plane of the base body, of the semiconductor light emitting device; and the semiconductor light emitting device has, at a position over the light emission region, a reflection mirror from which the light is reflected downwardly. With this method of fabricating a display unit, it is possible to provide the display unit capable of effectively directing light from the light emission region to the lower end plane of the semiconductor light emitting device by means of the reflection mirror.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein the semiconductor light emitting device is formed into a pyramid shape or a truncated pyramid shape; and any one of at least tilt planes among planes of the pyramid or truncated pyramid shaped semiconductor light emitting device is taken as the reflection mirror. With this method of fabricating a display unit, it is possible to provide the display unit capable of concentrating light emitted from the light emission region to the lower end plane of the semiconductor light emitting device by using the tilt planes of the polygonal pyramid or the truncated polygonal pyramid as the reflection mirrors or using the upper plane of the truncated polygonal pyramid as the reflection mirror.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein the semiconductor light emitting device is made from a gallium nitride based semiconductor having a hexagonal system; and the semiconductor light emitting device includes an active layer formed in parallel to a (1-101) plane. With this method of fabricating a display unit, since the gallium nitride based semiconductor exhibits a high light emission efficiency at the (1-101) plane, it is possible to provide the display unit having an excellent light emission characteristic.
According to an embodiment of the invention, there is provided a method of fabricating a display unit, wherein the semiconductor light emitting device is made from a gallium nitride based semiconductor formed by crystal growth on a growth substrate into a hexagonal pyramid shape or a truncated hexagonal pyramid shape with a (0001) plane taken as the lower end plane and (1-101) planes and planes equivalent thereto taken as the tilt planes; and the semiconductor light emitting device includes an active layer formed in parallel to the (1-101) planes and planes equivalent thereto. With this method of fabricating a display unit, since light emission is concentrated to the lower end plane of the semiconductor light emitting device with an electrode plane provided on the (1-101) plane parallel to the active layer exhibiting a high light emission efficiency taken as the reflection mirror, it is possible to provide the display unit having an excellent light emission characteristic.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures.